1. Field of the Invention
This invention relates to a method and apparatus for determining the electrostatic force present in an object, more particularly to a method and apparatus in which the electrostatic force is determined in terms of the weight of standardized testing membranes.
2. Description of the Related Art
Fibrous materials, such as non-woven fabrics, used as filter media in air filters, respirators or the like are electrostatically charged for efficient collection of dusts and other microparticles. The dust collecting properties of such a filter medium depends on the sufficiency of the electrostatic force present therein. Electrostatic force is however unfavorable for fibrous materials which are used as absorbent materials in diapers, feminine hygiene products, etc., and should be removed or reduced to a minimum. It is therefore important for manufacturers to evaluate or inspect the level of electrostatic force present in such fibrous materials in order to ensure good quality of their products.
Generally, expensive electrical instruments are used in conventional methods of measuring electrostatic forces. In an example of these methods, a capacitor-type probe is used as a detector for detecting electrostatic charges, and the detected signals are converted and amplified via additional electronic parts. While the instrument used in this method is sensitive and can provide accurate results, the construction thereof is complicated and the results thereof can be readily influenced by the surrounding conditions, such as the temperature, humidity, and the distance between the probe and the article to be tested. It is not economical to use such an instrument for testing and inspecting the electrostatic forces of products which are mass-produced and which do not require accuracy.